Question

(a) Explain the mechanism of a nucleophilic attack on the carbonyl group of an aldehyde or a ketone.
(b) An organic compound (A) (molecular formula C₈H₁₆O₂ ) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid also produced (B). On dehydration (C) gives but-1-ene. Write the equations for the reactions involved.

Answer 1

(a) Mechanism of nucleophilic addition reactions:
A nucleophile attacks the electrophilic carbon atom of the polar carbonyl group from a direction approximately perpendicular to the plane of sp² hybridized orbitals of carbonyl carbon. The hybridization of carbon changes from sp² to sp³ in this process and a tetrahedral intermediate is produced. The intermediate captures a proton from the medium to give the neutral product.

(b) The hydrolysis of the given compound with dil H₂SO_{4 t}o give a carboxylic acid and an alcohol suggests that the compound is an ester.